Process for separation of hydrogen and oxygen produced from photocatalytic water splitting by absorption

ABSTRACT

Embodiments of the invention are directed to methods, processes, and systems for safely and reliably purifying hydrogen from a gas mixture containing hydrogen and oxygen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/335,382 filed May 12, 2016, which is herebyincorporated by reference in its entirety.

BACKGROUND

Hydrogen fuel production has gained increased attention as oil and othernonrenewable fuels become increasingly depleted and expensive. Methodssuch as photocatalytic water-splitting are being investigated to producehydrogen fuel, which burns cleanly, and can also be used in a hydrogenfuel cell. Water-splitting holds particular interest since it utilizeswater, an inexpensive renewable resource.

Technologies are currently under development for producing energy fromrenewable and sustainable resources such as water. Water can be used asa feedstock for photocatalytic splitting using sun light to split watermolecules into hydrogen and oxygen. The process produces a highlyexplosive gas mixture, which requires using as yet defined techniquesand/or systems to separate and purify hydrogen from oxygen.

Various attempts to separate hydrogen from a product stream generatedfrom a water-splitting reaction have been described. By way of example,U.S. Pat. No. 4,233,127 to Monahan describes collecting dissociatedhydrogen and oxygen from a hot water splitting reaction (e.g., 2760° C.to 4150° C.), and separating the collected gases using a permeablemembrane or a separator tank positioned as close to the reaction zone aspossible to separate the gases at temperatures a high as possible toinhibit recombination of the gases.

While various methods to separate a gases mixture of hydrogen and waterfrom a water-spitting reaction have been described, there remains a needfor additional methods, processes, and systems for separating hydrogenfrom a highly flammable gaseous mixture containing hydrogen and oxygen.

SUMMARY

Embodiments of the current disclosure relate to methods, processes, andsystems that provide solutions to the problems associated with purifyinga gaseous mixture of hydrogen and oxygen produced by a photocatalyticwater-splitting process. The solution provides safe and reliable methodsfor separating hydrogen from a highly flammable and explosive gascontaining hydrogen and oxygen using solvent adsorption at atmosphericpressure.

Certain embodiments are directed to processes for separating hydrogenand oxygen from a gas mixture produced from photocatalytic splitting ofwater or other methods. A process can include: (a) compressing a feedsource gas that includes oxygen and hydrogen to at least 1 MPa (10 bar)at ambient temperature; (b) pressurizing a solvent to at least 1 MPa atambient temperature, wherein the solvent is capable of selectivelyadsorbing oxygen when under a pressure of at least 1 MPa (10 bar); (c)separating hydrogen and oxygen present in the feed source by solventadsorption comprising, (i) passing the compressed solvent through anadsorption column at a pressure of at least 1 MPa; and (ii) passing thecompressed feed source through an adsorption column at a pressure of atleast 1 MPa counter to the pressurized solvent, the pressurized solventselectively adsorbing oxygen from the feed source producing an enrichedhydrogen product gas and an oxygen enriched solvent; and (iii)separating the hydrogen product gas and the oxygen enriched solvent; and(d) collecting, storing, or utilizing the hydrogen product gas. Theprocess can further include (e) depressurizing the oxygen enrichedsolvent and desorbing the adsorbed oxygen from the solvent forming anoxygen off gas and regenerating the adsorption solvent; and (f)collecting, storing, or utilizing the oxygen off gas. In a furtheraspect, the process can also further include obtaining the feed sourcefrom a photocatalytic water-splitting reaction. In certain aspects, thefeed source is approximately 70 mol. % hydrogen, 25 mol. % oxygen, and 5mol. % carbon dioxide. In certain aspects, the solvent can be methanol,dimethyl ether of polyethylene glycol (DEPG), N-methyl-2-pyrrolidone(NMP), or propylene carbonate. The ambient temperature can be between15, 20, 25, 30, 35 and 40, 45, 50, or 60° C., including all values andranges there between. In a further aspect, the ambient temperature isbetween 15 and 60° C. The adsorption process can be performed at 0, 10,20, 30 to 40, 50, 60, or 70° C., or any value or range there between. Incertain aspects, the adsorption process can be performed at 0 to 60° C.In a further aspect, the adsorption process can be performed at about 20to 40° C. The feed source gas can be compressed to about, at least, orat most 1.0, 2.0, 3.0 to 3.0, 4.0, 5.0 MPa. In certain aspects, the feedsource gas can be compressed to about 2.0 MPa. In a further aspect, thefeed source gas is compressed to about 3.0 MPa. The solvent can becompressed to about, at least, or at most 1.0, 2.0, 3.0 to 3.0, 4.0, 5.0MPa. In certain aspects, the solvent is pressurized to about 2.0 MPa. Ina further aspect, the solvent can be pressurized to about 3.0 MPa. Theadsorption process can be performed at a pressure of about 1.0, 2.0,3.0, to 3.0, 4.0, 5.0 MPa. In certain aspects, the adsorption processcan be performed at a pressure of about 1.0 to 5.0 MPa. In a furtheraspect, the adsorption process is performed at a pressure of about 3.0MPa. The desorption process can be performed at a pressure of about0.05, 0.1, 0.2, or 0.4 MPa. In certain aspects, the desorption processcan be performed at a pressure of about 0.1 MPa. The process can furtherinclude filtering and dehydrating the feed source prior to feeding thefeed source gas to the adsorption column. In certain aspects, theprocess can be performed under conditions and using equipment tominimize spark generation. In a further aspect, the adsorption column isa packed column type adsorption column.

In certain aspects, the enriched hydrogen product gas can include atleast 90, 95, 98, or up to 99 mol. % hydrogen.

Other embodiments are directed to a purified hydrogen stream produced bya process as described herein. In certain aspects, the purified hydrogenstream can include at least 90, 95, 98, or 99 mol. % hydrogen.

Still other embodiments are directed to a purified oxygen streamproduced by a process as described herein. In certain aspects, thepurified oxygen stream can include at least 30, 40, 50, or 60 mol. %oxygen.

Certain embodiments are directed to a gas purification system that caninclude: (a) an adsorption column configured to (i) receive a feedsource gas in the lower half of the column so that the feed gas travelsup the column, and (ii) receive a solvent in the upper half of thecolumn so that the solvent travels down the column, wherein the solventselectively adsorbs oxygen and exits the column as an oxygen enrichedsolvent and the feed source gas is processed while traversing the columnand exits the top of the column as a hydrogen product gas; (b) a solventreservoir or source configured to provide lean solvent to the adsorptioncolumn; and (c) a feed gas source configured to provide a feed sourcegas to the adsorption column. The system can further include a solventregeneration unit configured to depressurize and deoxygenate a richsolvent exiting the adsorption column forming an oxygen off gas. Thesystem can further include a hydrogen storage device to collect andstore at least a portion of the enriched hydrogen stream. In certainaspects, the system further includes an oxygen storage device to collectand store at least a portion of the oxygen off gas.

The following includes definitions of various terms and phrases usedthroughout this specification.

The use of the words “a” or “an” when used in conjunction with any ofthe terms “comprising,” “including,” “containing,” or “having” in theclaims, or the specification, may mean “one,” but it is also consistentwith the meaning of “one or more,” “at least one,” and “one or more thanone.”

The terms “about” or “approximately” are defined as being close to asunderstood by one of ordinary skill in the art. In one non-limitingembodiment, the terms are defined to be within 10%, preferably within5%, more preferably within 1%, and most preferably within 0.5%.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or the alternativesare mutually exclusive, although the disclosure supports a definitionthat refers to only alternatives and “and/or.”

The terms “wt. %”, “vol. %”, or “mol. %” refers to a weight, volume, ormolar percentage of a component, respectively, based on the totalweight, the total volume of material, or total moles, that includes thecomponent. In a non-limiting example, 10 grams of component in 100 gramsof the material is 10 wt. % of component.

The term “substantially” and its variations are defined to includeranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” orany variation of these terms, when used in the claims and/or thespecification includes any measurable decrease or complete inhibition toachieve a desired result.

The term “effective,” as that term is used in the specification and/orclaims, means adequate to accomplish a desired, expected, or intendedresult.

The words “comprising” (and any form of comprising, such as “comprise”and “comprises”), “having” (and any form of having, such as “have” and“has”), “including” (and any form of including, such as “includes” and“include”) or “containing” (and any form of containing, such as“contains” and “contain”) are inclusive or open-ended and do not excludeadditional, unrecited elements or method steps.

The processes, methods, and systems of the present invention can“comprise,” “consist essentially of,” or “consist of” particularingredients, components, compositions, etc. disclosed throughout thespecification. With respect to the transitional phase “consistingessentially of,” in one non-limiting aspect, a basic and novelcharacteristic of the processes, methods, and systems of the presentinvention are their ability to separate hydrogen from a highlyflammability mixture of hydrogen and oxygen.

Other objects, features and advantages of the present invention willbecome apparent from the following figures, detailed description, andexamples. It should be understood, however, that the figures, detaileddescription, and examples, while indicating specific embodiments of theinvention, are given by way of illustration only and are not meant to belimiting. Additionally, it is contemplated that changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description. Infurther embodiments, features from specific embodiments may be combinedwith features from other embodiments. For example, features from oneembodiment may be combined with features from any of the otherembodiments. In further embodiments, additional features may be added tothe specific embodiments described herein.

DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofthe specification embodiments presented herein.

FIG. 1. A block diagram of one embodiment of a hydrogen purificationsystem disclosed herein of the present invention.

DESCRIPTION

A discovery has been found that provides a solution to handling highlyflammable mixtures produced from water-splitting processes. The solutionis premised on using a solvent adsorption process or system to separatehydrogen from a highly flammable and explosive gaseous mixturecontaining hydrogen and oxygen at ambient temperatures. The solution canprovide a hydrogen stream that includes at least 95 mol % hydrogen. Thecombination of a solvent adsorption system with a photocatalyticwater-splitting system provides the advantage of being able to separatea highly flammable mixture of oxygen and hydrogen generated from aphotocatalytic water-splitting system.

These and other non-limiting aspects of the present invention arediscussed in further detail in the following sections with reference tothe FIG. 1. The systems and methods of described in FIG. 1 can alsoinclude various equipment that is not shown and is known to one of skillin the art of chemical processing. For example, some controllers,piping, computers, valves, pumps, heaters, thermocouples, pressureindicators may not be shown.

A. Photocatalytic Water-Splitting

Photocatalytic water-splitting is the light-induced conversion reactionof water to hydrogen and oxygen. This reaction has attracted attentionas one of the most promising hydrogen production processes.Photocatalytic water-splitting is an artificial process for thedissociation of water into its constituent parts, hydrogen (H₂) andoxygen (O₂), using either artificial or natural light without producinggreenhouse gases or having many adverse effects on the atmosphere. WhenH₂O is split into O₂ and H₂, the stoichiometric ratio of its products is2:1. The process of water-splitting is a highly endothermic process(ΔH>0). Production of hydrogen from water requires large amounts ofinput energy, making it incompatible with existing energy generation.

There are several requirements for a photocatalyst to be useful forwater-splitting. The minimum potential difference (voltage) needed tosplit water is 1.23 eV at 0 pH. Since the minimum band gap forsuccessful water-splitting at pH=0 is 1.23 eV the electrochemicalrequirements can theoretically reach down into infrared light, albeitwith negligible catalytic activity. These values are true only for acompletely reversible reaction at standard temperature and pressure (1bar and 25° C.). Theoretically, infrared light has enough energy tosplit water into hydrogen and oxygen; however, this reaction iskinetically very slow because the wavelength is greater than 380 nm. Thepotential must be less than 3.0 eV to make efficient use of the energypresent across the full spectrum of sunlight. Water-splitting cantransfer charges, but not be able to avoid corrosion for long termstability. Defects within crystalline photocatalysts can act asrecombination sites, ultimately lowering efficiency.

Materials used in photocatalytic water-splitting fulfill the bandrequirements and typically have dopants and/or co-catalysts added tooptimize their performance. A sample semiconductor with the proper bandstructure is titanium dioxide (TiO₂). However, due to the relativelypositive conduction band of TiO₂, there is little driving force for H₂production, so TiO₂ is typically used with a co-catalyst such asplatinum (Pt) to increase the rate of H₂ production. It is routine toadd co-catalysts to spur H₂ evolution in most photocatalysts due to theconduction band placement. Most semiconductors with suitable bandstructures to split water absorb mostly UV light; in order to absorbvisible light, it is necessary to narrow the band gap.

Photocatalysts can suffer from catalyst decay and recombination underoperating conditions. In certain aspects catalyst decay becomes aproblem when using a sulfide-based photocatalyst such as cadmium sulfide(CdS), as the sulfide in the catalyst is oxidized to elemental sulfur atthe same potentials used to split water. Thus, sulfide-basedphotocatalysts are not viable without sacrificial reagents such assodium sulfide to replenish any sulfur lost, which effectively changesthe main reaction to one of hydrogen evolution as opposed towater-splitting. Recombination of the electron-hole pairs needed forphotocatalysis can occur with any catalyst and is dependent on thedefects and surface area of the catalyst; thus, a high degree ofcrystallinity is required to avoid recombination at the defects.Non-limiting Examples of photocatalyst NaTaO₃:La-NaTaO₃:La,K₃Ta₃B₂O₁₂—K₃Ta₃B₂O₁₂,(Ga_(0.82)Zn_(0.18))(N_(0.82)O_(0.18))—(Ga_(0.82)Zn_(0.18))(N_(0.82)O_(0.18)),and TiO₂-based systems.

NaTaO₃:La—NaTaO₃:La yields the highest water-splitting rate ofphotocatalysts without using sacrificial reagents. This UV-basedphotocatalyst was shown to be highly effective with water-splittingrates of 9.7 mmol/h and a quantum yield of 56%. The nanostep structureof the material promotes water-splitting as edges functioned as H₂production sites and the grooves functioned as O₂ production sites.Addition of NiO particles as co-catalysts assisted in H₂ production;this step can be done by using an impregnation method with an aqueoussolution of Ni(NO₃).6H₂O and evaporating the solution in the presence ofthe photocatalyst.

K₃Ta₃B₂O₁₂—K₃Ta₃B₂O₁₂ is activated by solely UV light and above, doesnot have the performance or quantum yield of NaTaO₃:La. However, it doeshave the ability to split water without the assistance of co-catalystsand gives a quantum yield of 6.5% along with a water-splitting rate of1.21 mmol/h. This ability is due to the pillared structure of thephotocatalyst, which involves TaO₆ pillars connected by BO₃ triangleunits.

(Ga_(0.82)Zn_(0.18))(N_(0.82)O_(0.18))—(Ga_(0.82)Zn_(0.18))(N_(0.82)O_(0.18))has one of the highest quantum yield in visible light for visiblelight-based photocatalysts that do not utilize sacrificial reagents. Thephotocatalyst gives a quantum yield of 5.9% along with a water-splittingrate of 0.4 mmol/h. Tuning the catalyst is done by increasingcalcination temperatures for the final step in synthesizing thecatalyst. Temperatures up to 600° C. helped to reduce the number ofdefects, though temperatures above 700° C. destroyed the local structurearound zinc atoms and was thus undesirable.

Pt/TiO₂—TiO₂ is a very efficient photocatalyst, as it yields both a highquantum number and a high rate of H₂ gas evolution. For example, Pt/TiO₂(anatase phase) is a catalyst used in water-splitting. Thesephotocatalysts combine with a thin NaOH aqueous layer to make a solutionthat can split water into H₂ and O₂. TiO₂ absorbs only ultraviolet lightdue to its large band gap (>3.0 eV), but outperforms most visible lightphotocatalysts because it does not photocorrode as easily. Most ceramicmaterials have large band gaps and thus have stronger covalent bondsthan other semiconductors with lower band gaps.

Cobalt based systems—Photocatalysts based on cobalt have been reported.Members are tris(bipyridine) cobalt(II), compounds of cobalt ligated tocertain cyclic polyamines, and certain cobaloximes. Chromophores havereportedly been connected to part of a larger organic ring thatsurrounded a cobalt atom. The process is less efficient than using aplatinum catalyst, cobalt is less expensive, potentially reducing totalcosts. The process uses one of two supramolecular assemblies based onCo(II)-templated coordination as photosensitizers and electron donors toa cobaloxime macrocycle.

B. Hydrogen Purification Using Solvent Adsorption

The gas produced from the photocatalytic water-splitting process is atnear atmospheric pressure and it can contain about 70% mol H₂, 25% molO₂ and 5% mol CO₂ This gas, is compressed to increase the pressure ofthe gas to the desired delivery pressure. The compressor, for example,is a piston compressor, a diaphragm compressor, a scroll compressor, orother type of compressor. In certain aspects, the gas is compressedusing a piston compressor. In certain aspects, the gas is compressed toapproximately 1 to 3 MPa (10 to 30 bar) and sent to a solvent adsorptionseparation unit for gas separation. For safety, the compressor should bea spark-free or spark-suppressed compressor.

Compressed gas can be used as a medium in numerous applications. Amongvarious known techniques for compression of gas, piston compressorsconstitute a specific example of compression devices. A gas compressoris a mechanical device that increases the pressure of a gas by reducingits volume. In certain aspects, the compressor has an inlet and anoutlet that are controlled by valves. At intake of gas into thecylinder, the inlet valve is opened and the outlet valve is closed. Whenthe cylinder is filled with gas, the inlet is closed, while the outletremains closed. The gas is then compressed to achieve an appropriatepressure and the outlet valve is opened through which the compressed gasis led. The compression cycle is repeated. Various compressor types canbe used, such as diaphragm type compressors, which can be obtainedthrough PDC Machines (Warminster, Pa.) or Howden & Sundyne (Arvada,Colo.) for example; or an ionic liquid filled compressor, which can beobtained from Linde (Pittston, Pa.) for example; or a labyrinth sealpiston compressor, which can be obtained from Burckhardt Compression(Houston, Tex.) for example.

For the process described herein, the gas exiting the photochemicalreactor is compressed to approximately 1.0 to 3.0 MPa before beingpassed through a feed/product exchanger and entering the bottom of theadsorption column.

The absorption column can be configured as a tray column, packed column,spray tower, bubble column, or a centrifugal contactor. In certainaspects, the gas mixture flows upward through a section of packing,contacting the solvent counter current, which enables the oxygen in thegas stream to dissolve into the solvent. The hydrogen rich gas streamexits the top. The solvent exits the column at the bottom, rich inoxygen, i.e., a rich solvent. The solvent can be depressurizedregenerating the solvent and releasing a gaseous oxygen (O₂) stream (offgas). The oxygen dissolved in the solvent can be recovered. In order tomaximize this recovery, recycling of the off gas may be needed.

After safely compressing the gas and producing the feed source, the feedsource can be sent to a solvent adsorption separation unit. Theprocessing chamber or column in the solvent adsorption separation unitcan be designed to allow hydrogen gas to selectively pass through thechamber or column, exiting on the product gas side. The oxygen or otherimpurities are absorbed in the solvent, exiting as a rich solvent. Theoff gas produced by the solvent absorption separation unit containsmainly oxygen. In certain aspects, a small amount of inert gas can beadded to reduce processing hazards.

In certain aspects, the hydrogen gas isolated by the solvent absorptionseparation unit can be further purified, if needed, by combustion. Thehydrogen rich gas (product gas) can be compressed (e.g., to 3.0 MPa) andtransmitted to a hydrogen purification unit. The hydrogen purificationunit processes the hydrogen rich gas by combustion, which removesresidual oxygen from the stream forming a purified stream. The purifiedstream is hot and can be used to raise medium pressure steam, whilecooling the gas stream down to remove water.

Hydrogen has a wide flammability range in comparison with other fuels.As a result, hydrogen can be combusted over a wide range of gasmixtures. Thus, hydrogen can combust in a mixture in which the gascontent is less than the theoretical, stoichiometric or chemically idealamount needed for combustion. Hydrogen has very low ignition energy. Theamount of energy needed to ignite hydrogen is about one order ofmagnitude less than that required for gasoline.

The potential for an explosive atmosphere during the processes disclosedherein will require the whole separation process to have zone 0classification (minimizing spark generation). Pipework and membranes aremade of a good electrical conducting polymer for the prevention ofsparks.

FIG. 1 illustrates a flow diagram for one embodiment of the system. Thesolvent absorption column 102 separates and removes selected gases,particularly oxygen, using a solvent absorption process. FIG. 1illustrates a scheme where reactants (e.g., water and sacrificial agent)and catalyst are processed in a reactor to produce a feed source stream101 that includes a mixture of hydrogen and oxygen. The feed source 101is compressed and transferred to bottom portion of absorption column102. In absorption column 102, the feed source is exposed to a countercurrent solvent under pressure such that hydrogen passes withoutsignificant absorption by the pressurized solvent forming a hydrogenrich permeate gas, or product gas. The lean solvent is supplied into theabsorption column 102, and absorbs oxygen from the feed sourcecontaining hydrogen. The processed feed source from which selected gaseshave been removed, is collected from the top of absorption column 102.After gas absorption, the rich solvent is discharged from the bottomportion of absorption column 102, and is regenerated by one or moredepressurization units 104. The lean solvent can be pressurized bycompressor 106, pass through heat exchanger 108, and be reintroduced toabsorption column 102. The off gas, oxygen can be capture, stored, andutilized, or exhausted as needed.

Solvents found to be useful in the present invention are solvents thatdissolve oxygen at increased pressures or under specific conditions andhave a low hydrogen solubility at those same pressures or conditions.Examples of useful solvents include methanol, dimethyl ether ofpolyethylene glycol (DEPG), N-methyl-2-pyrrolidone (NMP), or propylenecarbonate.

The FIGURE is included to demonstrate preferred embodiments of theinvention. It should be appreciated by those of skill in the art thatthe techniques disclosed in the examples or figures represent techniquesdiscovered by the inventors to function well in the practice of theinvention, and thus can be considered to constitute preferred modes forits practice. However, those of skill in the art should, in light of thepresent disclosure, appreciate that many changes can be made in thespecific embodiments which are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention.

1.-20. (canceled)
 21. A process for separating hydrogen and oxygen froma gas mixture produced from photocatalytic splitting of watercomprising: (a) compressing a feed source gas comprising oxygen andhydrogen to at least 1.0 MPa at ambient temperature; (b) pressurizing asolvent to at least 1.0 MPa at ambient temperature, wherein the solventis capable of selectively adsorbing oxygen when under a pressure of atleast 1.0 MPa; (c) separating hydrogen and oxygen present in the feedsource by solvent adsorption comprising, (i) passing the compressedsolvent through an adsorption column at a pressure of at least 1.0 MPa;and (ii) passing the compressed feed source gas through an adsorptioncolumn at a pressure of at least 1.0 MPa counter to the pressurizedsolvent, the pressurized solvent selectively adsorbing oxygen from thefeed source gas producing an enriched hydrogen product gas and an oxygenenriched solvent; and (iii) separating the hydrogen product gas and theoxygen enriched solvent; and (d) collecting, storing, or utilizing thehydrogen product gas; wherein the solvent comprises dimethyl ether ofpolyethylene glycol.
 22. A hydrogen product gas produced by the processof claim
 21. 23. A gas purification system comprising: (a) an adsorptioncolumn configured to (i) receive a feed source gas in the lower half ofthe column so that the feed gas travels up the column, and (ii) receivea solvent in the upper half of the column so that the solvent travelsdown the column, wherein the solvent selectively adsorbs oxygen andexits the column as an oxygen enriched solvent and the feed source gasis processed while traversing the column and exits the top of the columnas a hydrogen product gas; and (b) a solvent reservoir or sourceconfigured to provide lean solvent to the adsorption column; and (c) afeed gas source configured to provide a feed source gas to theadsorption column.
 24. The gas purification system of claim 23, whereinthe solvent comprises dimethyl ether of polyethylene glycol.
 25. Theprocess gas purification system of claim 23, wherein the feed source gasconsists of 70 mol % hydrogen, 25 mol % oxygen, and 5 mol % carbondioxide.
 26. The process gas purification system of claim 23, furthercomprising a solvent regeneration unit configured to depressurize anddeoxygenate solvent exiting the adsorption column to produce oxygen offgas.
 27. The process gas purification system of claim 23, furthercomprising a hydrogen storage device to collect and store at least aportion of the hydrogen product gas.
 28. The process gas purificationsystem of claim 23, wherein the absorption column is a tray column, apacked column, spray tower, bubble column, or a centrifugal contactor.29. The process gas purification system of claim 3, wherein theabsorption column is selected from the group consisting of a traycolumn, a packed column, spray tower, bubble column and a centrifugalcontactor.
 30. The process gas purification system of claim 23, whereinthe adsorption column is a packed column.
 31. The process gaspurification system of claim 23, wherein the adsorption column is a traycolumn.
 32. The process gas purification system of claim 23, wherein theadsorption column is a spray tower.
 33. The process gas purificationsystem of claim 23, wherein the adsorption column is a bubble column.34. The process gas purification system of claim 23, wherein theadsorption column is a centrifugal contactor.
 35. The process gaspurification system of claim 23, wherein the feed source is compressedand transferred to the lower half of the absorption column.
 36. Theprocess gas purification system of claim 23, further comprising adepressurization unit to regenerate the solvent from the oxygen enrichedsolvent.
 37. The process gas purification system of claim 23, whereinthe process gas purification system is zone 0 classified to minimizespark generation.
 38. The process gas purification system of claim 23,wherein the solvent exits at the lower half of the adsorption column.39. The process gas purification system of claim 23, further comprisinga recovery unit to recover oxygen from the oxygen enriched solvent. 40.The process gas purification system of claim 26, further comprising anoxygen storage device to collect and store at least a portion of theoxygen off gas.